1. Field of the Invention
The present invention relates to a substrate processing apparatus for applying a coating solution to a substrate such as a semiconductor wafer, an LCD glass substrate and so on and processing it.
2. Description of the Related Art
Generally, the photolithography technique in manufacturing process of a semiconductor device is performed by a series of processes such that a resist solution that is a coating solution is applied to the front surface of a substrate, such as a semiconductor wafer (hereinafter, referred to as a wafer), a resist film formed by the application of the solution is exposed to light according to a predetermined circuit pattern, and the exposed pattern is subjected to developing treatment to form a desired circuit pattern in the resist film.
In the above-described resist coating treatment, a spin chuck being a holding means rotatably holds a wafer, and the resist solution is supplied to the center of the front surface of the rotated wafer so that the resist solution on the wafer is spread by a centrifugal force by the rotation, whereby a uniform resist film is formed on the front surface of the wafer.
However, a problem with, in particular, a large-sized wafer (for example, a wafer having a size of 300 mm or larger) is that when the number of rotations is increased, the circumferential speed is increased and accordingly the resist solution dries more faster due to evaporation of a solvent to make the film thickness at the outer peripheral portion thicker, resulting in nonuniform film thickness.
As means to solve the above problem, a coating technique is known in which a gas having a kinematic viscosity coefficient higher than that of air, for example, helium (He) gas is supplied to a treatment space in which the resist solution is supplied to the rotated wafer so as to reduce a variations in uniformity of the film thickness at the wafer outer periphery (Claims in Japanese Patent Application Laid-open No. 3-245870).
Another method (apparatus) is also known in which the resist coating treatment is performed in a state in which an inert gas, for example, nitrogen (N2) gas, helium (He) gas or the like is introduced into the resist coating chamber to bring the pressure in the resist coating chamber to be higher than the atmospheric pressure, or into a positive pressure (Claims and FIG. 1 in Japanese Patent Application Laid-open No. 10-74688, and Claims and FIG. 4 in Japanese Patent Application Laid-open No. 2002-118051).